...Moby Dick first published early 1850s, but begins "Some years ago -- never mind how long precisely"; so Melville's setting presumably 1820s-40s. Imprecision, I think deliberate, one of the hallmarks of that odd narrative [which I may be perhaps the only person round here ever to have actually read it right thru]. It is eg never clear at any point just how long they have been at sea, and seldom just whereabouts on the globe they are!